Two teenagers, 15, have been arrested after breaking into an empty middle school in Denver.
Police say the two juveniles were carrying what appeared to be long rifles when they entered Noel Middle School at about 10pm last night.
They were arrested about five hours later after standoff.
Earlier police had surrounded the building and a bomb squad was called to the scene over concerns the men had explosives and were laying devices.
Officers saw the pair wearing backpacks and holding a large yellow pipe, according to reports.
Two cleaners called police shortly after 10pm local time after seeing two men inside the building.